ER-Model(Entity Relationship Model)
DBMS is a group of similar data information which is inserted organization table that is known as an entity. A model that represent the relations between the entities that known as ER-Model. The ER-Model introduced by PP Chen that represents the logical structure of database architecture. The overall structure can also represent a graphical format that is known as ER-Diagram.
Components of ER-diagram
- Entity-> An entity is the class of objects that allow accessing the data table. An entity helps us to represent the data members of the database.
- Attribute-> Each entity can have a number of characteristics that identity as an attribute. An entity can contain a set of attributes.
- Entity set-> It is the collection of the entity of similar type we create set of similar type. we create set of the entity of sharing the attributes between them.
- Relationship-> It is the relation between entities with the help of its attributes. An entity is easily identified into the database for processing.
- One to one relationship-> It is the relationship that allows creating link between two entity, with the help of relationship we can process entities with the similar field.
- one too many relationship->– It is a way to relate a single table with multiple entities. It means the entities are associated with single entities through a common field.
- Many to Many relationship-> They are multiple tables relate to multiple entities with the common field it is basically used to control multiple entities together.
Symbol of ER-Model
ER-Model provide built-in symbol of representing the entities and component like attributes like attributes relationship etc
Database design using ER-model
ER-model is using to represent entity on its components so we can design the database table and use the database record maintenance. ER-model completely represents entity columns and relationship between the given entity.
Strong and weak entity
Entity and together and independent also. The dependent entity is dependent on another entity that known weak entity and the independent entity knew as a strong entity. Every weak entity set can be converted to strong. An entity set by adding a particular attribute. The weak entity represents a double rectangle.
Superclass and Subclass
class->It is a way to create a group of data member like function entity etc. It helps us to manage the data and components into group format. It is the feature of the object-oriented database. We can also reuse the data member using class.
Object-> It is the instance of a class that allows to execute and access the data member of the particular class. Object use a memory to store information of the class.
Inheritance-> It is a process that allows to instances the feature of entity and class and another entity. It means we can share the attributes of an entity into a different entity.
Super class->It is the type of class entity that standard at other class. It is also known as a base class.
Sub class->It is a class that extends the feature of base class and able to excess the attribute. It is also known as desire class.
Attributes in inheritance
It is properties of higher and lower level entity that create by specialization and generalization. The attributes of entity sets are extended at other entity sets that manage in super and subclass or higher and lower level entity. This method basically uses to share the data member of the class to different class.
It is a process that manages the attribute inheritance into the entity. It represents the stored attribute into ER diagram through a rectangle component and level with “ISA”. It is the result of the particular lower level entity set to produces higher level as union form.
It is a process of sub-classes of an entity type. This type identifies subclass and specialization. The sets of a superclass are defined on the base of characterization of the entity in the superclass as specialization.
It is a process that complaining information and object thereby abstract and higher level object. In yan diagram relationship and not express as aggregation form. This process basically uses to manage the relationship and aggregated the attribute inheritance.
This process managed in object-oriented system develop records into superclass and subclass. The data member is categorized into a different class and help to excess with help of an object. The manage the attribute and its processing.